What is FODMAP? A plain-English guide

FODMAP is an acronym for a group of short-chain carbohydrates and sugar alcohols: Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols. The term was developed by researchers at Monash University in Australia, who were investigating why certain carbohydrates trigger gut symptoms in people with irritable bowel syndrome.

The short version: FODMAPs are carbohydrates that some people's small intestines can't absorb well. They pass into the large intestine, where gut bacteria ferment them — producing gas, drawing in water, and causing the bloating, cramping, and altered bowel habits that characterise IBS.

The five FODMAP groups

Not all FODMAPs behave the same way, and not everyone reacts to all of them. The five groups are:

• Oligosaccharides — fructans (found in wheat, garlic, onion) and galacto-oligosaccharides (found in legumes). Humans lack the enzyme to digest these entirely.
• Disaccharides — primarily lactose, found in dairy. Requires the enzyme lactase to digest; lactase levels vary significantly between people.
• Monosaccharides — specifically excess fructose (found in honey, apples, high-fructose corn syrup). Absorbed poorly when present in greater amounts than glucose.
• Polyols — sugar alcohols like sorbitol and mannitol (found in stone fruits, some vegetables, and many sugar-free products). Absorbed slowly and incompletely.

The fermentable part of the acronym matters: all five groups are fermented by gut bacteria, which is what produces the gas and triggers symptoms.

Serving size changes everything

One of the most important and counterintuitive aspects of FODMAPs is that most foods aren't simply "high" or "low" — they exist on a spectrum determined by how much you eat. A small amount of avocado is low-FODMAP. A large portion isn't. A handful of almonds is fine. A larger serving pushes past the threshold.

This is why FODMAP tracking requires logging quantities, not just ingredients. "I had avocado" is not useful data. "I had 50g of avocado" is.

Who the low-FODMAP diet is for

The low-FODMAP diet is specifically designed for people with IBS. It isn't a general wellness diet, a weight-loss protocol, or a recommendation for people without gut symptoms. Research consistently shows it reduces symptoms in around 70–75% of IBS patients — but it's a structured diagnostic process, not a way of eating indefinitely.

The goal is to identify your personal triggers through a systematic elimination and reintroduction protocol — then return to eating as broadly as possible while avoiding only the foods that specifically cause you problems.